You’ve heard of the canary in the coal mine – if it stops singing there’s trouble for the miners. The doc The Messenger coopts that scenario, arguing that as we hear fewer songbirds, we should assume the earth is suffering.

Director Su Rynard’s mission is to find eco-activist bird protectors to explain why songbirds’ numbers have decreased dramatically. Among the culprits: noise pollution that prevents them from hearing mating calls, light pollution that forces them off course and lights left on in office buildings so birds think they can fly right through the windows and are killed.

According to FLAP Canada, the city of Toronto has over 950,000 registered buildings that could potentially kill over 9 million birds each year. One activist counted 500 dead birds over six hours at two structures alone.

Humans, via our excessive consumption, among other things, are the worst killers, of course – a shot of a French gourmand snacking on a fried ortolan is devastating. But are you a cat lover? Well, felines are among the worst predators.

The Messenger doesn’t bust conventional doc format and it sounds earnest, I know, but it doesn’t come across that way. The loving passion of these activists makes a huge impression, and the birds themselves are spectacular.